MAL-2026-5539 Malicious code in mermaid-v11 (npm)

The package impersonates the legitimate mermaid diagramming library (name mermaid-v11, bogus version 9999.0.2, description 'Mermaid v11 diagramming library') and ships no library code — only a malicious preinstall lifecycle hook. On npm install, package.json line 6 runs node -e that reads require('os').hostname() and the OS username and beacons them out-of-band to an attacker-controlled Interactsh endpoint via two channels: an HTTPS GET to https://d8l0dj5t5p5il86s3d3gepriqucsnn1nd.oast.me/?h=<hostname>&u=<username>&pkg=mermaid-v11, and a DNS lookup of mermaid-v11.<hostname>.d8l0dj5t5p5il86s3d3gepriqucsnn1nd.oast.me to leak the hostname through the resolver chain. The behavior fires automatically on default install with no user interaction, harvesting installer host identifiers for an attacker-controlled OAST listener.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

The OpenSSF Package Analysis project identified 'mermaid-v11' @ 9999.0.2 (npm) as malicious.

It is considered malicious because:

• The package communicates with a domain associated with malicious activity.